1. Field of the Invention
The invention relates to electrochemical cells for lithium/solid polymer electrolyte batteries. More particularly, the invention concerns electrochemical cells based on a lithium anode and a solid polymer electrolyte, and with lateral current collection, including a band of insulating material disposed so as to prevent the free edge of the collector which faces the electrolyte and/or the layer of negative electrode from cutting through the electrolyte and/or from short-circuiting the two electrodes. The invention also concerns a process for preparing electrochemical cells in which the free edge of the collector is protected by a band of insulating material.
2. Description of Prior Art
The general principle of polymer electrolyte batteries of the ACEP type (polymer electrolyte battery) and lithium anode is described in Armand U.S. Pat. No. 4,303,748. The materials preferably used in these batteries (copolymers, cross-linked polymers, salts, active materials for the electrodes) as well as the methods for preparing them are described, inter alia, in U.S. Pat. Nos. 4,578,326 and 4,758,487.
An ACEP battery consists of a metallic collector for the positive electrode (cathode), a film of a cathode, a film of a polymer electrolyte, a film of a negative electrode (lithium anode) and an insulating film. Each of these films typically has a thickness between 5 and 50.mu., for a total final thickness between 100 and 150.mu., about thirty meters of film, 15 cm wide being typically necessary to give a battery of 100 Wh. Different types of possible assembly for these different components are described in U.S. applications Ser. Nos. 337,522 filed Feb. 21, 1989, now U.S. Pat. No. 5,100,746, and 342,538 filed Feb. 21, 1989, now abandoned. An appropriate way of assembly consists in slightly offsetting each of these films, so as to be able to laterally collect the current which originates from each of the electrodes, as in a condenser, rather than through the ends of the film. In this arrangement, one of the edges of the collector is used to collect the current which comes from the cathode. The other edge which will hereinafter be referred to as the free edge of the collector, faces the electrolyte and/or the negative electrode, following an offset mounting. Such an assembly causes the following problem: the metallic collector of the positive electrode (cathode) is generally made of a foil of aluminum, nickel or another metal which, even at low thickness, has a free cutting edge which is capable of directly contacting the negative electrode or of cutting through the layer of electrolyte, consisting of a relatively flexible polymer, and to thereby cause a short-circuit with the lithium anode, leading to the destruction of the battery.